Method for producing carbon black

ABSTRACT

In a carbon black manufacturing process a method is provided whereby the off-gas from at least one carbon black manufacturing process is utilized both to lower the temperature of the hot combustion gases and to provide some heat to the hot combustion gases by being burned in the combustion tunnel of a carbon black reactor. A portion of the off-gas is utilized while still holding the total volume of the hot combustion gases substantially constant at a preselected substantially constant temperature to insure a substantially constant quality of carbon black.

This application is a divisional of application Ser. No. 946,654, filedOct. 2, 1978 now U.S. Pat. No. 4,237,092.

This invention relates to carbon black production. In a specific aspectthis invention relates to method for using off-gas from at least onecarbon black manufacturing process to lower the temperature of thecombustion gases in a carbon black manufacturing process. In anotherspecific aspect this invention relates to method for using off-gas toprovide some combustion heat to the combustion gases in the carbon blackprocess. In still another aspect this invention relates to method forusing off-gas to provide some combustion heat to the combustion gases inthe carbon black process while holding the total volume of hotcombustion gases constant at a preselected temperature.

When combusting a combustible fuel, with about a stoichiometric amountof oxygen, in a combustion tunnel before introduction of the resultingcombustion gases into the carbon black combustion chamber, it has beenfound that the temperature of the combustion gases can exceed atemperature which will damage the refractory lining of the combustiontunnel. To prevent the temperature of the combustion gases fromexceeding a temperature which will damage the refractory lining of thecombustion tunnel it has been common in the past to introduce excessoxygen or air to reduce the temperature of the combustion gases.However, if excess oxygen is provided for combustion, then the excessoxygen will oxidize a portion of the carbonaceous feed and therebyreduce the yield of carbon black.

In more recently developed carbon black production systems, the off-gasfrom a carbon black manufacturing process is utilized to lower thetemperature of the combustion gases produced from combustion of a fuelusing about a stoichiometric amount of oxygen. The off-gas from a carbonblack manufacturing process contains substantially no oxygen and thusvery little excess oxygen is introduced into the carbon black reactor bythe off-gas. The off-gas from a carbon black manufacturing processcontains some hydrogen and carbon monoxide which can be used to providesome combustion heat to the combustion gases by being burned in thecombustion tunnel, thus reducing the use of the more expensive high BTUfuel used in the carbon black process.

While some previous systems have utilized the off-gas from a carbonblack manufacturing process to lower the temperature of the combustiongases and as a source of additional heat in the combustion chamber, theproblem of using the off-gas from a carbon black manufacturing processwhile still maintaining a constant quality of carbon black has not beenaddressed. When the off-gas from a carbon black process is utilized toprovide some combustion heat to the combustion chamber, additionaloxygen or air must be introduced into the combustion tunnel to maintaina stoichiometric amount of oxygen in the combustion tunnel. Alsoshrinkage of the off-gas from the carbon black process will occur as thehydrogen and carbon monoxide are burned in the combustion tunnel. Thiswill affect (decrease) the total volume of hot combustion gases which isprovided to the carbon black reaction chamber, thus affecting thequality of the carbon black being produced if steps are not taken tomaintain the total volume of the hot combustion gases constant whileusing the off-gas from a carbon black process to lower the temperatureof the combustion gases and as a source of additional heat in thecombustion chamber.

It is thus an object of this invention to provide method for usingoff-gas from a carbon black process to lower the temperature of thecombustion gases in the carbon black process. Another object of thisinvention is to provide method and apparatus for using off-gas toprovide some combustion heat to the combustion gases in the carbon blackprocess. Still another object of this invention is to provide method andapparatus for using off-gas to provide some combustion heat to thecombustion gases in the carbon black process while holding the totalvolume of hot combustion gases substantially constant at a preselectedtemperature.

In accordance with the present invention, method and apparatus isprovided whereby off-gas from at least one carbon black process issupplied to the combustion tunnel of the carbon black reactor.Sufficient air is introduced into the combustion tunnel to maintain astoichiometric relationship between the fuel gas, including the off-gas,in the combustion tunnel of the carbon black reactor. The flow ofoff-gas to the carbon black combustion tunnel is controlled so as tomaximize the use of the off-gas while still maintaining the total volumeof hot combustion gases substantially constant at a preselectedsubstantially constant temperature. This is accomplished by manipulatingboth the flow of the primary fuel gas and the flow of the off-gas insuch a manner that the total volume of hot combustion gases produced bysubstantially stoichiometric combustion of the fuel gas and off-gas isconstant at a preselected substantially constant temperature whenshrinkage due to combustion of hydrogen and carbon monoxide in theoff-gas is taken into account.

The off-gas from a carbon black filter or the cooled smoke from upstreamof the filter can be utilized to quench the carbon black reaction in thecarbon black reaction chamber. The flow of off-gas or cooled smoke as aquench fluid to the carbon black reaction chamber is controlled in sucha manner that a desired temperature in the carbon black reaction chamberis maintained which will provide the desired carbon black product.

Other objects and advantages of the invention will be apparent from thedetailed description of the invention and the appended claims as well asfrom the detailed description of the drawings in which:

FIG. 1 is a schematic representation of the apparatus used for producingcarbon black in the present invention together with the associatedcontrol system for the carbon black process; and

FIG. 2 is a schematic representation of the computer logic utilized toprocess the measured data provided to the computer to provide the setpoints required by the control system illustrated in FIG. 1.

For the sake of simplicity the invention is illustrated and described interms of a single carbon black reactor having a single reaction chamber.The invention, however, is applicable to multiple carbon black reactorsand is also applicable to carbon black reactors having multiplecombustion chambers.

Although the invention is illustrated and described in terms of aspecific carbon black reactor and a specific control configuration, theapplicability of the invention described herein extends to other typesof carbon black reactors and also extends to different types of controlsystem configurations which accomplish the purpose of the invention.Lines designated as signal lines in the drawings are electrical in thispreferred embodiment. However, the invention is also applicable topneumatic, mechanical, hydraulic, or other signal means for transmittinginformation. In almost all control systems some combination of thesetypes of signals will be used. However, use of any other type of signaltransmission, compatible with the process and equipment in use, iswithin the scope of the invention.

Controllers shown may utilize the various modes of control such asproportional, proportional-integral, proportional-derivative, orproportional-integral-derivative. In this preferred embodimentproportional-integral controllers are utilized. The operation of thesetypes of controllers is well known in the art. The output control signalof a proportional-integral controller may be represented as

    S=K.sub.1 E+K.sub.2 ∫EDt

where

S=output control signal;

E=difference between two input signals; and

K₁ and K₂ are constants.

The various transducing means used to measure parameters whichcharacterize the process and the various signals generated thereby maytake a variety of forms of formats. For example, the control elements ofthe system can be implemented using electrical analog, digitalelectronic, pneumatic, hydraulic, mechanical or other similar types ofequipment or combinations of one or more of such equipment types. Whilethe presently preferred embodiment of the invention preferably utilizesa combination of pneumatic control elements, such as pneumaticallyoperated valve means in conjuction with electrical analog signalhandling and translation apparatus, the apparatus and method of theinvention can be implemented using a variety of specific equipmentavailable to and understood by those skilled in the process control art.Likewise the format of the various signals can be modified substantiallyin order to accommodate signal format requirements of the particularinstallation, safety factors, the physical characteristics of themeasuring or control instruments and other similar factors. For example,a raw flow measurement signal produced by differential pressure orificeflow meter would ordinarily exhibit a generally proportionalrelationship to the square of the actual flow rate. Other measuringinstruments might produce a signal which is proportional to the measuredparameter, and still other transducing means may produce a signal whichbears a more complicated, but known relationship to the measuredparameter. In addition, all signals could be translated into a"suppressed zero" or other similar format in order to provide a "livezero" and prevent an equipment failure from being erroneouslyinterpreted as a "low" or "high" measurement or control signal.Regardless of the signal format or the exact relationship of the signalto the parameter which it represents, each signal representative of ameasured process parameter or representative of a desired process valuewill bear a relationship to the measured parameter or desired valuewhich permits designation of a specific measured or desired value by aspecific signal value. A signal which is representative of a processmeasurement or a desired process value is therefore one from which theinformation regarding the measured or desired value can be readilyretrieved regardless of the exact mathematical relationship between thesignal units and the measured or desired process units.

Referring now to the drawings and in particular in FIG. 1, a carbonblack reactor 11 having a combustion tunnel 12, combustion orprecombustion chamber 13, and a reaction chamber 14 is illustrated. Acarbonaceous feed is supplied to the carbon black combustion chamber 13through conduit means 16. Fuel gas and off-gas from the separationmeans, which is preferably a bag filter 28 is supplied to the carbonblack combustion tunnel 12 through conduit means 18. The hot combustiongases produced in the carbon black combustion tunnel 12 are introducedinto the carbon black combustion chamber 13 preferably in a generallytangential manner, with respect to the carbon black reaction chamber 14,so as to effect a vortex flow of the hot combustion gases along thelength of the carbon black reaction chamber 14. The hot combustion gasesintroduced from the carbon black combustion tunnel 12 contact thecarbonaceous feed at a temperature sufficiently high to pyrolyze asubstantial portion of the carbonaceous feed to carbon black particles.After a predetermined length of reaction time, depending mainly ondesired photelometer, the effluent flowing through the reaction chamber14 is quenched by contact with cooled smoke from the heat exchanger 23which is introduced into the reaction chamber 14 through conduit means31. It is noted that other quench fluids can be used such as water.However, the use of the cooled smoke from the heat exchanger 23 isdesirable in that the filter 28 is not required to handle the largeamounts of water vapor which will be produced if water is used as thequench fluid.

The effluent from the carbon black reaction chamber 14, which containsthe carbon black particles and other gases is supplied through conduitmeans 21 to the filter 28. In a preferred embodiment of the inventionthe heat exchanger 23 is operably connected to conduit means 21 to coolthe effluent from the carbon black reaction chamber 14 before it entersthe filter 28. The filter 28 is utilized to separate the carbon blackparticles from the gaseous portion of the effluent. The carbon blackparticles separated by the filter 28 are provided through conduit means25 to a processing, such as pelleting. The separated gaseous portion,which has been referred to as off-gas in the description of the presentinvention, can be recycled at least in part to be used as a quench fluidfor the reaction chamber 14 and can be also utilized as a quench fluidfor the combustion tunnel 12 as well as providing heat to the combustionchamber 13. The off-gas can be provided through conduit means 33 toconduit means 31 and passed to conduit means 35. Any unused portion ofthe off-gas is vented through control valve 37 located in conduit means33. The off-gas is provided to conduit means 18 which is operablyconnected to the combustion tunnel 12 through conduit means 35. Air orother oxygen containing gas required to supply a stoichiometric amountof oxygen to burn the hydrogen and carbon monoxide in the off-gas issupplied through conduit means 41. Conduit means 41 is operablyconnected to conduit means 18.

A high BTU fuel is provided through conduit means 43 and conduit means18 to the combustion tunnel 12. Preferably a stoichiometric amount ofoxygen required to burn the high BTU fuel is provided through conduitmeans 45 and conduit means 18 to the combustion tunnel 12. In thispreferred embodiment of the invention, methane is utilized as the highBTU fuel but other suitable fuels can also be used in the carbon blackprocess. Preferably air is utilized to provide the oxygen required tocombust the high BTU fuel in the combustion tunnel 12.

It is common for a number of carbon black reactors to be operated in acommon facility. In plants where a number of carbon black reactors areemployed the off-gas from other carbon black filters can be supplied tothe combustion tunnel 12 through conduit means 47 which is operablyconnected to conduit means 35. In like manner any off-gas or othermaterial having combustible material flowing through control valve 37may be supplied to a combustion tunnel of other carbon black reactors.

Control of the flow rate of the carbonaceous feed through conduit means16 is accomplished by means of pneumatic control valve 51 located inconduit means 16. The flow rate of the carbonaceous feed through conduitmeans 16 is measured by flow sensor 52 which transmits a signal 53,representative of the flow rate of the carbonaceous feed in conduitmeans 16, to flow transducer 55. Flow transducer 55 supplies a signal56, representative of the flow rate of the carbonaceous feed in conduitmeans 16, to flow controller 58 and multiplying means 64. Flowcontroller 58 is also supplied with a set point signal 59,representative of the desired flow rate of the carbonaceous feed throughconduit means 16. Signal 60, representative of a comparison of theactual and desired flow rates of the carbonaceous feed through conduitmeans 16, is supplied as a control signal from flow controller 58 topneumatic control valve 51.

Multiplying means 64 is also supplied with a signal 63, representativeof the BTU/gallon required to convert the carbonaceous feed to thedesired carbon black product. Signal 66, which is supplied bymultiplying means 64, is thus representative of the BTU/hr. required toconvert the carbonaceous feed to the desired carbon black product.Signal 66 is supplied as an input to computer means 75 and is alsosupplied as an input to dividing means 68. Dividing means 68 is alsosupplied with a signal 67, representative of the difference between theactual temperature of the hot combustion gases in the combustion tunnel12 and a base temperature, with the difference (ΔT) being multiplied bythe specific heat (C_(P)) of the combustion gases. Signal 69,representative of the total volume of hot combustion gases which must besupplied to the combustion chamber 13 to maintain a desired temperaturein the combustion chamber 13, is supplied from dividing means 68 as aninput to computer means 75.

The flow of the off-gas through conduit means 31 to the reaction chamber14 is controlled by means of pneumatic flow controller 81. Thetemperature in the reaction chamber 14 is measured and is transmitted assignal 84 by temperature transducer 83. Signal 84 is supplied fromtemperature transducer 83 to temperature controller 86. Temperaturecontroller 86 is also supplied with a set point signal 87,representative of the desired temperature at the outlet end of thereaction zone 14. Signal 89 which is representative of a comparison ofthe actual and desired temperatures at the outlet end of the reactionchamber 14 is supplied from temperature controller 86 to pneumaticcontrol valve 81. The pneumatic control valve 81 is manipulated inresponse to signal 89 to thereby control the flow rate of the off-gasthrough conduit means 31 to the reaction chamber 14 to thereby maintaina desired temperature at the outlet end of the reaction chamber 14 wherethe carbon black reaction is quenched.

The flow rate of the high BTU fuel gas through conduit means 43 iscontrolled by pneumatic control valve 91 which is located in conduitmeans 43. Flow sensor 93 senses the flow rate of the high BTU fuel gasthrough conduit means 43 and a signal 95, representative of the actualflow rate of the high BTU fuel gas through conduit means 43, istransmitted to flow controller 98 from flow transducer 94. Flowcontroller 98 is also supplied with a set point signal 99 representativeof the desired flow rate of the high BTU fuel gas through conduit means43. The desired flow rate signal 99 is calculated by computer means 75in response to the process variables input to computer means 75. Signal99 is supplied from computer means 75 to the flow controller 98. Signal101, representative of a comparison of the actual and desired flowrates, is provided to pneumatic control valve 91 from flow controller98. Pneumatic control valve 91 is manipulated in response to signal 101to thereby maintain the flow rate of the high BTU fuel gas throughconduit means 43 at a desired level. The high BTU fuel gas flowingthrough conduit means 43 is analyzed by analyzer transducer 104 todetermine the BTU content of the fuel gas. The analyzer transducer 104may be a chromatographic analyzer or other suitable analyzer capable ofmeasuring the BTU content of a fuel gas. Signal 105, representative ofthe BTU content of the fuel gas flowing through conduit means 43, issupplied from analyzer transducer 104 as an input to computer means 75.The temperature of the high BTU fuel gas flowing through conduit means43 is measured and is transmitted as signal 114 to computer means 75 bytemperature transducer 112.

The flow of air through conduit means 45 is controlled by pneumaticcontrol valve 121. The actual flow rate of the air flowing throughconduit means 45 is measured by flow sensor 123. Signal 126,representative of the actual flow rate of the air flowing throughconduit means 45, is transmitted by temperature transducer 124 to flowcontroller 127. Flow controller 127 is also supplied with a set point129, representative of the flow rate of air required to provide astoichiometric amount of oxygen for the high BTU fuel gas in thecombustion tunnel 12. The set point signal 129 is calculated bysupplying signal 95, representative of the actual flow rate of the fuelgas through conduit means 43, and signal 137, representative of therequired ratio between the flow rate of the air through conduit means 45and the flow rate of the high BTU fuel gas through conduit means 43, tomultiplying means 133. Multiplying means 133 supplies signal 129 to flowcontroller 127. Temperature transducer 138 provides a signal 139,representative of the temperature of the air flowing through conduitmeans 45, to computer means 75.

The flow rate of the off-gas flowing through conduit means 35 iscontrolled by pneumatic control valve 141. Flow sensor 143 measures theactual flow rate of the off-gas flowing through conduit means 35. Signal146, representative of the actual flow rate of the off-gas flowingthrough conduit means 35, is transmitted from flow transducer 144 toflow controller 148. Flow controller 148 is also supplied with a setpoint signal 149 which is representative of the desired flow rate of theoff-gas through conduit means 35. Signal 149 is calculated by computermeans 75 in response to the process variables input to the computermeans 75. Signal 149 is transmitted from computer means 75 to the flowcontroller 148. Signal 151, representative of a comparison of the actualand desired flow rates of the off-gas through conduit means 35, issupplied from flow controller 148 to pneumatic control valve 141.Pneumatic control valve 141 is manipulated in response to signal 151 tothereby maintain the flow rate of the off-gas through conduit means 35at a required level.

Analyzer transducer 153 is utilized to analyze the off-gas flowingthrough conduit means 35 and to provide three output signals to computermeans 75. Signal 155 from analyzer transducer 153 is representative ofthe hydrogen content in the off-gas flowing through conduit means 35.Signal 157 is representative of the carbon monoxide content of theoff-gas flowing through conduit means 35. Signal 159 is representativeof the BTU content of the off-gas flowing through conduit means 35. Thetemperature of the off-gas flowing through conduit means 35 is providedas signal 163 to computer means 75 by temperature transducer 161.

The flow of air through conduit means 41 is controlled by pneumaticcontrol valve 171. The actual flow rate of the air flowing throughconduit means 41 is measured by flow sensor 173. Signal 175,representative of the actual flow rate of the air flowing throughconduit means 41, is supplied by flow transducer 174 to flow controller178. Flow controller 178 is also supplied with a set point signal 177,representative of the required flow rate of air necessary to supply astoichiometric volume of oxygen for the off-gas flowing through conduitmeans 35. Signal 177 is calculated by multiplying means 183. Signal 146,representative of the actual flow rate of off-gas through conduit means35 is supplied to multiplying means 183. Multiplying means 183 is alsosupplied with a signal 185, representative of the required ratio of airto off-gas. Signal 185 is calculated by computer means 75 in response tothe process variables input to computer means 75. Signal 146 ismultiplied by signal 185 to provide signal 177. Signal 179, which isrepresentative of a comparison of the actual and desired flow rates ofthe air through conduit means 41, is supplied as the control signal topneumatic control valve 171. Pneumatic control valve 171 is manipulatedin response to signal 179 to thereby maintain the flow rate of the airthrough conduit means 41 at a desired level. Temperature transducer 187provides a signal 189, representative of the temperature of the airflowing through conduit means 41, to computer means 75.

A number of electronic and/or pneumatic systems can be used toautomatically calculate the set point signals 99, 149, and 185 which areprovided by computer means 75 in the preferred embodiment of theinvention illustrated in FIG. 1. The set point signals 99, 149 and 185could also be calculated by hand if desired. FIG. 2 illustrates, inanalog form, the computer logic required to calculate the set pointsignals 99, 149 and 185.

The following development of the set points 99, 149 and 185, utilized inthe present invention, is provided to clarify the analog developmentillustrated in FIG. 2. The volume of off-gas required may be determinedby ##EQU1## where V_(OG) =total volume of off-gas required (SCF/HR);

H_(T) =total heat required (BTU/HR);

V_(T) =total volume of hot combustion gases required (SCF/HR);

H_(FG) =heat added by burning one standard cubic foot (SCF) of fuel gasstoichiometrically with air plus the sensible heat of the fuel gas andair determined at a base temperature of 60° F. divided by the SCFproduced by the burning of the 1 SCF of fuel gas in a stoichiometricamount of air;

H_(OG) =heat added by burning one SCF of off-gas stoichiometrically withair plus the sensible heat of the off-gas and air determined at a basetemperature of 60° F.; and

B_(OG) =the SCF of off-gas burned with air stoichiometrically to produceone SCF of hot combustion gases.

The value of H_(FG) in equation (1) may be determined by ##EQU2## whereH_(CFG) =heat of combustion of fuel gas, (BTU/SCF);

T_(FG) =temperature of fuel gas, (°F.);

C_(PFG) =specific heat of fuel gas, at T_(FG), (BTU/SCF/°F.);

R₁ =volume ratio of air to fuel gas, (stoichiometric combustion);

T_(AFG) =temperature of air supplied for fuel gas, (°F.);

C_(PAFG) =specific heat of air at T_(AFG) supplied for fuel gas(BTU/SCF/°F.); and

V_(HG) =SCF produced by the burning one SCF of fuel gas in astoichiometric amount of air.

The value of H_(OG) in equation (1) may be determined by

    H.sub.OG =H.sub.COG +(T.sub.OG -60)(C.sub.POG)+R.sub.2 (T.sub.AOG -60)(C.sub.PAOG)                                          (3)

where

H_(COG) =heat of combustion of off-gas, (BTU/SCF);

T_(OG) =temperature of off-gas, (°F.);

C_(POG) =specific heat of off-gas at T_(OG) (BTU/SCF/°F.);

R₂ =volume ratio of air to off-gas (Stoichiometric combustion);

T_(AOG) =temperature of air supplied for off-gas, (°F.);

C_(PAOG) =specific heat of air supplied for off-gas, at T_(AOG)(BTU/SCF/°F.).

The value of B_(OG) in equation 1 may be determined by

    B.sub.OG =1+S                                              (4)

where

S=shrinkage in SCF per SCF of off-gas stoichiometrically combined withair.

The value of R₂ in equation 3 may be determined by

    R.sub.2 =(Y+Z/40)                                          (5)

where

Y=volume percent CO in off-gas; and

Z=volume percent H₂ in off-gas.

The value of S in equation 4 may be determined by

    S=(Y+Z/50)                                                 (6)

where

Y and Z are as previously defined.

The volume of high BTU fuel gas required may be determined by ##EQU3##where V_(T), V_(OG), S, and V_(HG) are as previously defined.

The set point 185 provided to multiplying means 183 is equal to R₂ asdefined above and may be calculated by use of equation (5).

The symbols defined in the preceding paragraphs are used in thedescription of FIG. 2. Referring now to FIG. 2, signal 66 which isrepresentative of H_(T) is supplied as one input to subtracting means200. Signal 69, which is representative of V_(T), is supplied as oneinput to multiplying means 206 and subtracting means 208. Signal 105,which is representative of H_(CFG), is supplied as one input to summingmeans 215. Signal 114, which is representative of T_(FG), is supplied asone input to subtracting means 211. Subtracting means 211 is alsosupplied with signal 212, which is representative of the basetemperature (60° F.) for the computer calculations. Signal 218, which isrepresentative of (T_(FG) -60) is supplied as one input to multiplyingmeans 213. Multiplying means 213 is also supplied with signal 214, whichis representative of C_(PFG). Signal 219, which is representative of(T_(FG) -60) (C_(PFG)), is supplied from multiplying means 213 as asecond input to summing means 215. Signal 139, which is representativeof T_(AFG), is supplied as one input to subtracting means 222.Subtracting means 222 is also supplied with signal 221, which isrepresentative of the base temperature (60° F.) for the computercalculations. Signal 224, which is representative of (T_(AFG) -60), issupplied as one input from subtracting means 222 to multiplying means225. Multiplying means 225 is also supplied with signal 227, which isrepresentative of R₁. Signal 229, which is representative of (R₁)(T_(AFG) -60), is supplied as one input to multiplying means 231 frommultiplying means 225. Multiplying means 231 is also supplied withsignal 232, which is representative of C_(PAFG). Signal 234, which isrepresentative of R₁ (T_(AFG) -60) (C_(PAFG)), is supplied as a thirdinput to summing means 215 from multiplying means 231. Signal 235, whichis representative of H_(CFG) +(T_(FG) -60)(C_(PFG))+R₁ (T_(AFG)-60)(C_(PAFG)), is supplied as one input to dividing means 237. Dividingmeans 237 is also supplied with signal 238, which is representative ofV_(HG). Signal 239, which is representative of H_(FG), is supplied as asecond input to multiplying means 206. Signal 241, which isrepresentative of (V_(T)) (H_(FG)), is supplied as a second input tosubtracting means 200. Signal 244, which is representative of H_(T)-(V_(T)) (H_(FG)), is supplied as one input to dividing means 246.

Signal 159, which is representative of H_(COG), is supplied as one inputto summing means 251. Signal 163, which is representative of T_(OG), issupplied as one input to subtracting means 253. Subtracting means 253 isalso provided with a signal 254, which is representative of the basetemperature (60° F.) for the computer calculations. Signal 256, which isrepresentative of (T_(OG) -60), is supplied as an input to multiplyingmeans 258 from subtracting means 253. Multiplying means 258 is alsosupplied with signal 261, which is representative of C_(POG). Signal263, which is representative of (T_(OG) -60) (C_(POG)), is supplied as asecond input to summing mean 251 from multiplying means 258. Signal 188,which is representative of T_(AOG), is supplied as one input tosubtracting means 265. Subtracting means 265 is also supplied with asignal 267, representative of the base temperature (60° F.) for thecomputer calculations. Signal 269, which is representative of (T_(AOG)-60), is supplied as one input to multiplying means 271. Multiplyingmeans 271 is also supplied with signal 273, which is representative ofC_(PAOG). Signal 275, which is representative of (T_(AOG) -60)(C_(PAOG)), is supplied as one input to multiplying means 277 frommultiplying means 271. Signal 155, which is representative of Y, issupplied as one input to summing means 281. Signal 157, which isrepresentative of Z, is supplied as a second input to summing means 281.Signal 283, which is representative of Y+Z, is supplied to dividingmeans 286 and to dividing means 293. Dividing means 286 is also suppliedwith a signal 289, representative of a constant 40. Signal 185, which isrepresentative of (Y+Z)/40, is supplied as a second input to multiplyingmeans 277 and is also supplied as a set point to multiplying means 183illustrated in FIG. 1. Signal 185 was defined as R₂ in the equationswhich were previously developed.

Signal 279, which is representative of R₂ (T_(AOG) -60) (C_(PAOG)), issupplied as a third input to summing means 251 from multiplying means277. Signal 304, which is representative of H_(OG), is supplied as oneinput to subtracting means 315.

Dividing means 293 is also supplied with a signal 295, representative ofthe constant 50. Signal 297, representative of (Y+Z)/50, is supplied asone input to summing means 298. Summing means 298 is also supplied witha signal 299, representative of the constant +1. Signal 301, which isrepresentative of B_(OG), is supplied as an input to multiplying means311 from summing means 298. Signal 239, which is representative ofH_(FG), is also supplied to multiplying means 311. Signal 314, which isrepresentative of (B_(OG)) (H_(FG)), is supplied as a second input tosubtracting means 315. Signal 317, which is representative of H_(OG)-(B_(OG)) (H_(FG)), is supplied as a second input to dividing means 246.Signal 149 which is representative of V_(OG) is supplied from dividingmeans 246 as a set point to flow controller 148. Signal 149 is alsosupplied to multiplying means 321. Multiplying means 321 is alsosupplied with signal 301, which is representative of B_(OG). Signal 323,which is representative of (V_(OG)) (B_(OG)), is supplied as a secondinput to subtracting means 208. Signal 325, which is representative ofV_(T) -(V_(OG)) (B_(OG)), is supplied as one input to dividing means 327from subtracting means 208. Dividing means 327 is also supplied withsignal 329, which is representative of V_(HG). Signal 99, which isrepresentative of V_(FG), is supplied as a set point to flow controller98 illustrated in FIG. 1.

In the practice of the present invention the flow of air through conduitmeans 45 and 41 is controlled so as to provide a stoichiometric amountof oxygen in the combustion chamber 12. To produce certain types ofcarbon black, it is desirable to have excess oxygen so that partialoxidation of the make-hydrocarbon results. If excess oxygen is desiredit is simply necessary to modify the set point signal 137 supplied tomultiplying 133 to provide a higher amount of oxygen to the combustionchamber 12.

The temperature of the hot combustion gases in the combustion tunnel 12is held below a temperature which would damage portions of the carbonblack reactor 11 but the temperature is still sufficiently high toachieve pyrolysis of the carbonaceous feed. Refractory damagingtemperature is the temperature at which softening of the refractorylining occurs or the temperature at which spalling can be caused. Forexample, if the refractory is 90 percent alumina, the temperature of thehot combustion gases should be held below about 3100° F. for continuousoperation. If the refractory is chrome alumina, then the hot combustiongas temperature should be held below about 3500° F. for continuousoperation.

The temperature of the air entering through conduit means 45 and conduitmeans 41 will be dependent upon the particular process used andgenerally will be between about 100° F. and about 1200° F. Thetemperature of the high BTU gas which is supplied through conduit means43 will preferably be between 100° F. and 700° F. The temperature of theoff-gas flowing through conduit means 35 will preferably be below about700° F. and will preferably have an oxygen content of less than about0.5 percent by volume. This off-gas is preferably then preheated afterleaving the filter; e.g. from about 400° F. up to the highertemperature.

The following "calculated" examples are provided to illustrate possiblemodes of operation of a carbon black system incorporating the presentinvention. Methane is used as the high BTU fuel gas in the calculatedexamples. The methane, air and off-gas are all preheated to 660° F.

EXAMPLE I

    ______________________________________                                        Make-hydrocarbon feed rate                                                                         250 gal/hr.                                              BTU/GAL of oil required                                                                            41,800 BTU/GAL.                                          Total BTU/HR in hot gases (H.sub.T)                                                                10,450,000 BTU/HR                                        Total hot gases (V.sub.T)                                                                          128,000 SCF/HR                                           Required temperature in combustion                                                                 3200° F.                                          tunnel 12                                                                     Volume percent CO in off-gas (Y)                                                                   10%                                                      Volume percent H.sub.2 in off-gas (Z)                                                              10%                                                      Heat of combustion of off-gas (H.sub.COG)                                                          60 BTU                                                   Heat of combustion of fuel gas (H.sub.CFG)                                                         1000 BTU                                                 Air to fuel-gas ratio (R.sub.1)                                                                    10:1                                                     Air to off-gas ratio (R.sub.2)                                                                     0.5:1                                                    Required volume of off-gas (V.sub.OG)                                                              48,443 SCF/HR                                            Required volume of air for off-gas                                                                 24,222 SCF/HR                                            Required volume of methane                                                                         5,471 SCF/HR                                             Required volume of air for methane                                                                 54,710 SCF/HR                                            Volume of hot combustion gases                                                                     67,821 SCF/HR                                            contributed by off-gas                                                        Volume of hot combustion gases                                                                     60,181 SCF/HR                                            contributed by methane                                                        Total volume of hot combustion gases                                                               128,002 SCF/HR                                           ______________________________________                                    

EXAMPLE II

    ______________________________________                                        Make-hydrocarbon feed rate                                                                           250 gal/hr.                                            BTU/GAL of oil required                                                                              41,800 BTU/GAL.                                        Total BTU/HR in hot gases (H.sub.T)                                                                  10,450,000 BTU/HR                                      Total hot gases (V.sub.T)                                                                            128,000 SCF/HR                                         Required temperature in combustion                                                                   3200° F.                                        tunnel 12                                                                     Volume percent CO in off-gas (Y)                                                                     12%                                                    Volume percent H.sub.2 in off-gas (Z)                                                                12%                                                    Heat of combustion of off-gas (H.sub.COG)                                                            72 BTU                                                 Heat of combustion of fuel gas (H.sub.CFG)                                                           1000 BTU                                               Air to fuel-gas ratio (R.sub.1)                                                                      10:1                                                   Air to off-gas ratio (R.sub.2)                                                                       0.6:1                                                  Required volume of off-gas (V.sub.OG)                                                                52,467 SCF/HR                                          Required volume of air for off-gas                                                                   31,480 SCF/HR                                          Required volume of methane                                                                           4,577 SCF/HR                                           Required volume of air for methane                                                                   45,770 SCF/HR                                          Volume of hot combustion gases                                                                       77,651 SCF/HR                                          contributed by off-gas                                                        Volume of hot combustion gases                                                                       50,347 SCF/HR                                          contributed by methane                                                        Total volume of hot combustion gases                                                                 127,998 SCF/HR                                         ______________________________________                                    

As the volume percent of CO and H₂ in the off-gas changes the amount ofshrinkage of the off-gas in the combustion tunnel 12 also changes.However, as is illustrated in Examples I and II, even though the volumepercent of CO and H₂ in the off-gas and thus the heat of combustion ofthe off-gas changes, the control system of the present invention iscapable of maintaining a substantially constant temperature and asubstantially constant volume of hot combustion gases in the combustionchamber 13. Maintaining a constant temperature and a constant volume ofhot combustion gases is a major factor in producing carbon black of aconstant quality.

The invention has been described in terms of a preferred embodiment asis illustrated in FIGS. 1 and 2. Specific components which can be usedin the practice of the invention as illustrated in FIGS. 1 and 2 such ascontrollers 58, 86, 98, 127, 148 and 178; flow sensors 52, 93, 123, 143and 173; and associated flow transducers 55, 94, 124, 144 and 174;temperature transducers 83, 112, 138, 161, and 187; control valves 51,81, 91, 121, 141, and 171 are each well known commercially availablecontrol components such as are described at length in Perry's ChemicalEngineer's Handbook, 4th Edition, Chapter 22, McGraw-Hill.

Analyzer transducers 104 and 153 are in this preferred embodimentchromatographic analyzers. A suitable chromatographic analyzer is theOptichrom 2100 manufactured by Applied Automation, Bartlesville,Oklahoma. The multiplying means 64, 133, and 183 and the dividing means68 illustrated in FIG. 1 as well as the summing, subtracting,multiplying and dividing means illustrated in FIG. 2 are in thispreferred embodiment the number B05885 Multiuse Amp manufactured byApplied Automation, Bartlesville, Okla.

Also, for reasons of brevity and clarity, conventional auxiliaryequipment such as pumps for feed and fuel gases, additional heatexchangers, additional measurement-control devices, and additionalprocessing equipment required in carbon black production have not beenincluded in the above description as they play no part in theexplanation of the invention.

While the invention has been described in terms of the presentlypreferred embodiment, reasonable variations and modifications arepossible, by those skilled in the art, within the scope of the describedinvention and the appended claims. For example, the type of carbon blackbeing produced may require that the air to fuel gas ratio be held at ahigher ratio than that necessary to provide a stoichiometric amount ofoxygen in the combustion tunnel 12. Also the basic control methodillustrated in FIGS. 1 and 2 may frequently be used as a subsystem for amore comprehensive carbon black process control.

That which is claimed is:
 1. In a method for producing carbon blackcomprising the steps of:contacting hot combustion gases and acarbonaceous feed in a reaction zone to thereby produce carbon black andgas; separating said carbon black from said gas; and utilizing at leasta part of the thus separated gas as a recycle gas to supply at least apart of said hot combustion gases; the improvement comprising the stepof: maintaining the ratio of the volume of said hot combustion gases tothe volume of said carbonaceous feed substantially constant at a desiredtemperature for said hot combustion gases.
 2. A method in accordancewith claim 1 wherein said recycle gas is burned with a fuel and anoxygen containing gas in a combustion zone to supply said hot combustiongases and wherein said step of maintaining the ratio of the volume ofsaid hot combustion gases to the volume of said carbonaceous feedsubstantially constant at a desired temperature for said hot combustiongases comprises:controlling the flow of said oxygen containing gas tosaid combustion zone so as to maintain a desired ratio of said oxygencontaining gas to said fuel and a desired ratio of said oxygencontaining gas to said recycle gas; and controlling the flow of saidfuel and said recycle gas to said combustion zone so as to maintain theratio of the volume of said hot combustion gases to the volume of saidcarbonaceous feed substantially constant at a desired temperature forsaid hot combustion gases.
 3. A method in accordance with claim 2wherein said step of controlling the flow of said fuel to saidcombustion zone comprises:establishing a first signal representative ofthe actual flow rate of said fuel; establishing a second signalrepresentative of the desired flow rate of said fuel; comparing saidfirst signal and said second signal and establishing a third signalresponsive to the difference between said first signal and said secondsignal; and controlling the actual flow rate of said fuel in response tosaid third signal.
 4. A method in accordance with claim 3 wherein saidstep of controlling the flow of said recycle gas to said combustion zonecomprises:establishing a fourth signal representative of the actual flowrate of said recycle gas; establishing a fifth signal representative ofthe desired flow rate of said recycle gas; comparing said fourth signaland said fifth signal and establishing a sixth signal responsive to thedifference between said fourth signal and said fifth signal; andcontrolling the flow rate of said recycle gas in response to said sixthsignal.
 5. A method in accordance with claim 4 wherein first and secondflows of said oxygen containing gas are supplied to said combustionzone, said first flow of said oxygen containing gas maintaining adesired ratio of said oxygen containing gas to said fuel, said secondflow of said oxygen containing gas maintaining a desired ratio of saidoxygen containing gas to said recycle gas.
 6. A method in accordancewith claim 5 wherein said step of controlling the flow of said oxygencontaining gas to said combustion zone comprises:establishing a seventhsignal representative of the actual flow rate of said first flow of saidoxygen containing gas; establishing an eighth signal representative ofthe desired flow rate of said first flow of said oxygen containing gas;comparing said seventh signal and said eighth signal and establishing aninth signal responsive to the difference between said seventh signaland said eighth signal; controlling the flow rate of said first flow ofsaid oxygen containing gas in response to said ninth signal;establishing a tenth signal representative of the actual flow rate ofsaid second flow of said oxygen containing gas; establishing an eleventhsignal representative of the desired flow rate of said second flow ofsaid oxygen containing gas; comparing said tenth signal and saideleventh signal and establishing a twelfth signal responsive to thedifference between said tenth signal and said eleventh signal; andcontrolling the flow rate of said second flow of said oxygen containinggas in response to said twelfth signal.
 7. A method in accordance withclaim 6 wherein said oxygen containing gas is air, the desired ratio ofsaid oxygen containing gas to said fuel is a stoichiometric ratio, andthe desired ratio of said oxygen containing gas to said recycle gas is astoichiometric ratio.
 8. A method in accordance with claim 7 whereinsaid step of establishing said fifth signal comprises:establishing athirteenth signal (H_(T)) representative of the total heat desired ofsaid hot combustion gases; establising a fourteenth signal (V_(T))representative of the total volume of said hot combustion gases desired;establishing a fifteenth signal (H_(FG)) representative of the heatadded by burning one standard cubic foot of said fuel stoichiometricallywith said air plus the sensible heat of said fuel and said airdetermined at a base temperature of 60° F. divided by the standard cubicfeet produced by the burning of said fuel in a stoichiometric amount ofsaid air; multiplying said fourteenth signal and said fifteenth signalto establish a sixteenth signal representative of (V_(T)) (H_(FG));subtracting said sixteenth signal from said thirteenth signal toestablish a seventeenth signal representative of H_(T) -(V_(T))(H_(FG)); establishing an eighteenth signal representative of the heatadded by burning one standard cubic foot of said recycle gasstoichiometrically with said air plus the sensible heat of said recyclegas and said air determined at a base temperature of 60° F.;establishing a nineteenth signal representative of the standard cubicfeet of said recycle gas burned with said air stoichiometrically toproduce one standard cubic foot of said hot combustion gases;multiplying said fifteenth signal and said nineteeth signal to produce atwentieth signal representative of (B_(OG)) (H_(FG)); subtracting saidtwentieth signal from said eighteenth signal to produce a twenty-firstsignal representative of H_(OG) -(B_(OG)) (H_(FG)); and dividing saidseventeeth signal by said twenty-first signal to establish said fifthsignal.
 9. A method in accordance with claim 8 wherein said step ofestablishing said second signal comprises:multiplying said nineteenthsignal by said fifth signal to establishing a twenty-second signalrepresentative of (V_(OG)) (B_(OG)); subtracting said twenty-secondsignal from said fourteenth signal to establish a twenty-third signalrepresentative of V_(T) -(V_(OG)) (B_(OG)); establishing a twenty-fourthsignal (V_(HG)) representative of the standard cubic feet produced bythe burning of said fuel gas in a stoichiometric amount of said air; anddividing said twenty-third signal by said twenty-fourth signal toproduce said second signal.
 10. A method in accordance with claim 9wherein said step of establishing said eighth signalcomprises:establishing a twenty-fifth signal representative of thedesired ratio of said air to said fuel; and multiplying said firstsignal by said twenty-fifth signal to produce said eighth signal.
 11. Amethod in accordance with claim 10 wherein said step of establishingsaid eleventh signal comprises:establishing a twenty-sixth signalrepresentative of the desired ratio of said air to said recycle gas; andmultiplying said twenty-sixth signal by said fourth signal to producesaid eleventh signal.
 12. A method in accordance with claim 1additionally comprising the steps of:supplying at least a portion of thegas which has been seperated from said carbon black to said reactionzone as a quench fluid; and controlling the flow of said quench fluid tosaid reaction zone so as to maintain a desired quench temperature insaid reaction zone.
 13. A method in accordance with claim 12 whereinsaid step of controlling the flow rate of said quench fluid to saidreaction zone comprises:establishing a first signal representative ofthe actual quench temperature in said reaction zone; establishing asecond signal representative of the desired quench temperature in saidreaction zone; comparing said first signal and said second signal andestablishing a third signal responsive to the difference between saidfirst signal and said second signal; and controlling the flow rate ofsaid quench fluid to said reaction zone in response to said thirdsignal.